Short-wave keying device



June 8, 1943. P. F. BYRNE SHORT WAVE KEYING DEVICE Original Filed March 22, 1939 INVENTOR.

340 Eye! ATTORNEY.

Patented June 8, 1943 SHORT-WAVE KEYING DEVICE Paul F. Byrne, West Caldwell, N. J., assignor to Federal Telephone and Radio Corporation, a corporation of Delaware Original application March 22, 1939, Serial No. 263,367, now Patent No. 2,285,851, dated June 9, 1942. Divided and this application November 28, 1941, Serial No. 420,796

2 Claims.

My invention relates to high frequency transmission systems and more particularly to radio frequency transmission circuits adapted to supply energy to two or more symmetrical loads from an unsymmetrical source of supply or from a single symmetrical two conductor line or loop. This invention is a division of my copending application Serial No. 263,367, filed March 22, 1939, Patent No. 2,285,851, dated June 9, 1942, and entitled Short-wave transmitters.

It is often desirable to transmit energy from an unsymmetrical source such as an oscillator or frequency multiplier grounded on one side, to two or more symmetrical loads, for example, radiating antennae. This type of arrangement is particularly useful for supplying energy to trans mitting antennae which may be used for de fining a beacon course, since under these circumstances it is desirable that the load be properly balanced in order that the system be efficient and a suitable radiation pattern be secured. Furthermore, in beacon systems it is often desired to separately adjust the power fed to each of the radiating antennae, so that the course line may be properly defined and maintained. Similarly it may be desired to connect two or more balanced lines over which energy is transmitted to a single unbalanced line or to a single balanced line.

It is an object of my invention to provide a radio frequency transmission system which is suitable for intercoupling two or more balanced lines and an unbalanced line.

It is a further object of my invention to provide a radio transmitter in which energy from an unbalanced source is applied to a plurality of antennae each connected to a separate balanced line.

It is a further object of my invention to provide in a radio transmitter a system which permits the independent adjustment of energy to the separate balanced antennae.

It is a still further object of my invention to provide the combination of a radio frequency source, a balanced amplifier and a plurality of balanced loads connected to the output of the amplifier.

'It is a still further object of my invention to provide a radio transmitter with a balanced line feedfor two or more separate antennae, in which the energy fed to the antennae may be separately modulated orkeyed.

It is a still further object of my invention to provide a novelrkeying arrangement for use with a-pair of symmetrical radio beacon antennae.

whereas impedance I I2 is a condenser.

The above mentioned and further features and object of my invention and the manner of attaining them will be apparent from a particular description of my invention made in accordance with the accompanying drawing, in which Fig. 1 illustrates a preferred embodiment of a radio transmitter made in accordance with my invention,

Fig. 2 illustrates a form of split stator condenser suitable for use in the modulation system of Fig. 1, and

Fig. 3 illustrates an alternative modulation system in accordance with my invention which may be used in place of that disclosed in Fig. 1.

Turning now to the drawings and particularly to Fig. 1, Iiiil represents a source of radio frequency energy which may be, for example, an oscillator or a frequency multiplier. In source Hill at 102 is indicated a vacuum tube which may represent the last stage of the radio frequency circuit within I00. The anode of tube I82 is connected to a positive voltage supply as indicated, and is connected through the primary of transformer I33 to ground for radio frequencies through the radio frequency condenser IOI. Transformer I63 is designed for high frequencies and constitutes a single turn for the primary and secondary so that the coupling between the primary and secondary is made by means of a distributed inductance and capacity only. Cbupling transformer I03 is made adjustable so that the coupling between the windings may be varied.

The secondary of the transformer I03 is connected to ground on one side and on the other side to a transmission line I04, through a variable power controlling condenser I05. It is evident that this arrangement forms an unsymmetrical line portion. This unsymmetrical line is connected to a push-pull amplifier comprising vacuum tubes I06, Ill-1. Since, in order for the vacuum tubes to operate properly in push-pull the input thereto should be balanced, I provide a network to achieve this balance indicated generally at I08. At lower radio frequencies balanced input may be obtained by merely grounding the center point of a transformer and connecting the outer ends through lines to the grid. However, at higher frequencies balance cannot be obtained so simply. A balance may be obtained by connecting in series across the line a pair of impedances such as IIEI, III, and connecting these impedances to ground through a third impedance IIZ. In the circuit shown in Fig. 1, impedances H0 and III areinductanoes,

A balance may be obtained in this Way provided impedances H0, and III are properly related to impedance H2 in value and are of a sign opposite to that of H2. In the preferred arrangement impedances III) and III are made equal and impedance H2 is made equal to one-half the value of either of the impedances H0, or III. However, a considerable departure from this relationship may occur in practice, approximate equality of impedances H and III being sufficient, and a considerable variation in the relationship of the impedance values of H2 and H0, III being permissible for most applications. In order that a complete balance may be obtained inductances III! and III are arranged so as to have very little, if any, mutual coupling between them. A blocking condenser I I3 is provided between inductance III and the junction points of I II) and I I2, so that power may be supplied to the grid of tubes I36 and I 37 through the leads H4, H4 independently of each other. This arrangement permits the use of separate grid meters to indicate the operation of the tubes. The output circuit of the vacuum tubes I06, Hill, is connected to a high frequency variable transformer H5, the primary of which is connected to a power supply through radio frequency choke H6, Tuning condensers III are provided to tune the output of push-pull amplifier. Coupled to the secondary of transformer I I5 are conductors H8, H9, which together form a balanced output line. The separate conductors H8, H9, are unbalanced with respect to ground so that each conductor may be considered as a further unsymmetrical line. The midpoint of the secondary of transformer H5 is grounded so that in effect each of lines I I8 and I is may be considered as an independent unbalanced line with a ground return. In lines I I8, I I9, are provided variable condensers I20, I21, which may serve to independently control the power output over the respective lines.

In line II 8 is provided another high frequency network which serves to produce a balanced output from the unsymmetrical line H3. This network comprises inductance elements 22, I24, connected similar to inductance elements H0, and III, and to a variable condenser unit I28, corresponding to condenser H2. Condenser I26 is made variable so that its impedance may be adjusted to balance precisely transmission line I28. Similarly, line H9 is branched to form a balanced transmission line I29 through a network comprising inductance elements I23, and I25, and a variable capacity element I21.

To the outer end of transmission line I23 is coupled an antenna I30, shown as a dipole antenna, and to line I29 is coupled another dipole antenna I3I. While I have shown antenna I and I3 I, as dipoles, it should be distinctly understood that they may be of any desired form so long as they are designed to form a balanced load. Furthermore, it is clear that instead of leading to antennae, transmission lines I28 and I29 may lead to any desired type of symmetrical load.

If it is desired to use antennae I30 and I3I as a radio beacon, these antennae should be arranged at a suitable angle with respect to each other to produce the desired wave pattern. Arrangements of antennae for radio beacon transmission are well known so no specific illustration thereof is made in this application.

In order that the signals from the separate antennae may be distinguished, I provide means to modulate the energy fed to the antennae to form the distinctive signals. Any desired modulating means may be used as the method of modulation in such as to preserve the symmetry of the system. In the arrangement according to Fig. 1, I provide, for modulating the antennae, a filter, comprising resonant quarter wavelength frames I32 and I33 constituting sections of transmission line and loosely coupled to the transmission line. These frames are coupled to the transmission line inductively primarily through capacitive induction and may be precisely tuned by means of trimming condensers I34, I95. When these frames are properly positioned with respect to the transmission line and accurately tuned, they will operate to substantially stop all of the energy from flowing along the transmission line. Although I have illustrated these tuned coupled sections as open-ended frames, they may have other forms, such as closed frames of proper length or may be of various other formations. For structural details of the various forms of transmission modifying networks, reference may be had to Patent No. 2,159,648, issued May 23, 1939 on an application of Andrew Alford, Ser. No. 162,853 filed September 8, 1937. Since the filtering action of coupled transmission line sections, such as shown at I32 and I33 are very critical with tuning, their effect on the flow of energy through transmission lines I23, I29, may be modified by slightly detuning the section. This fact is made use of in producing the modulation of the energy transmitted to the antennae. Across each of networks I32, I33, I provide split-stator condensers I38, I31. These condensers are arranged with the fixed plates coupled to the separate conductors of the transmission line, while the rotary plates are driven at a uniform rate by means of a motor I40 or other means. Condensers I38 and I3! may be made with a different number of notches in the stator plate so that the energy flowing along transmission lines I28, I29 is interrupted at a difierent rate to impress a difierent modulation upon the energy radiated from antennae I30, I3I.

One form of split-stator condenser suitable for use in the system of Figure 1, is illustrated in Figure 2. This condenser comprises fixed toothed stators 20I, 202, connected to the opposite side of a balanced line 230, and a single rotary plate element 293. When 203 is rotated at a uniform rate the tuning of the condenser is varied periodically, depending upon the speed of the rotor 233 and the number of teeth on stator plates 2M, 202. Thus a chopping or keying of energy may be accomplished by means of this rotary condenser connected across a tuned frame such as I32. The frequency of modulation may be varied by varying the number of teeth on the condenser or by driving the rotors of the condensers at different speeds. The percentage or depth of modulation may be controlled by so choosing the condensers as to provide the desired preciseness of tuning of the coupledsections.

While in Fig. 1 I have illustrated the arrange ment wherein an amplifier is utilized between the source of radio frequency oscillation and the load, it should be distinctly understood thatthis amplifier may be omitted, and the energy and amplification taken care of in other parts of the circuit, if desired. Also, it should be understood that the balancing network need not be composed of two inductances and a single capac ity as shown, but may be of any form of impedance so long as they satisfy the requirement specified above. It is thus clear that in place of inductances H and III of I08, equal capacities should be substituted therefor and an inductance reaction used in place of condenser H2. However, I prefer to use the inductance arrangement since it permits a separate energization of the grid. Similarly, the impedance element in the network associated with the separate antennae circuit could be of different values if desired without altering the scope of my invention. It should further be understood, according to the general reciprocity theorem, that instead of a transmitter, the system may constitute a receiving arrangement. Antennae I30, I3I receive radio signals and transmit them over balanced lines to an unbalanced receiver. In Fig. 3, I have illustrated an alternative form of modulating system which may be substituted for that illustrated in Fig. 1. In this arrangement 320, 32], 318 and 319, represent the power adjusting condensers and the conductors of the transmission line similar to that disclosed in Fig. 1. Similarly the network comprises induotances 322, 32-4 and capacity 326, and inductances 323, 325, capacity 326, correspond to similar elements in Fig. 1. Loads 33!], 3| I, may be antennae corresponding to I30, I31 or any other form of symmetrical load. The modulating system, however, differs from that shown in Fig. 1. At 341, 342 are illustrated two half-wave length short circuited frames connected at the proper point across balanced transmission lines 328, 329, respectively. At a point midway of the length of transmission line sections SM, 342 are provided short circuiting switches 343, 344, which are driven by means of a, motor 340. Adjustable short circuiting bars 345, 346, are provided on each of the sections 34], 342.

This modulating system operates as follows: When a short circuiting switch 343 is crosswise so as to short circuit the network 34I, this network forms a short circuited quarter wavelength line connected across transmission line 328. Aside from resistance and radiation losses the circuit will not drain nor hamper flow of energy along transmission line to load 33!]. When switch 343 is turned to the open position the effective circuit from the transmission line extends out to the short-circuited end of the half-wavelength section 34!. This then constitutes a half-wavelength short circuited filter across the main line preventing substantially all of the energy from flowing to the antenna. Thus the modulation may be obtained by interrupting the flow of energy along the line by means of the short circuiting switch 343. Similarly modulations may be effected in the energy of line 329 by short circuiting switch 344. These switches may be provided with a plurality of segments so as to interrupt the flow at different rates in the two different lines so as to provide difierent modulations of the energy for the two loads. If it is desired to utilize less than modulation, short circuiting bars 345, 346 may be changed in position so as to alter the length of the section from that of a full half-wavelength.

While I have described my invention with references to figures illustrating a preferred embodiment thereof, it should be understood that this description is merely by way of illustration and not a limitation of the scope of my invention, which is defined in the accompanying claims.

What I claim is:

1. A radio frequency transmitter for operating at a particular frequency, comprising a source of radio frequency energy, a balanced transmission line coupled to said source, a section of transmission line substantially a, half wavelength or odd multiple of a half wavelength long bridged at one of its ends across said transmission line and short circuited at its remote end, and means for modulating the transmitted energy comprising a short circuiting means arranged at a distance equal to a quarter wavelength or odd multiple thereof from the junction of said section conductor and said balanced transmission line, and means for periodically connecting and disconnecting said short circuiting means across said section, said transmission line section including means for Varying the amount of modulation produced by said modulating means.

,2. A radio frequency beacon transmitter for operating at a. particular frequency, comprising a source of radio frequency energy, a pair of balanced transmission lines coupled to said source, a section of transmission line substantially a half wavelength or an odd multiple of a half wavelength long bridged at one of its ends across each of said transmission lines, and short circuited at its remote end, and means for modulating the energy in said transmission lines with distinguishing signals comprising a short circuiting means arranged at a distance equal to a quarter wavelength or an odd multiple thereof from the junction of each said section with its associated transmission line, and means for periodically connecting and disconnecting said short circuiting means across each of said sections at a different rate to alternately permit and substantially inhibit flow of energy along said lines, each said transmission line section including means for varying the amount of modulation produced by said modulating means.

PAUL F. BYRNE. 

